Impact resistant polymers can be produced by polymerizing a major amount of vinyl aromatic compounds with a minor amount of rubber. Many different types of vinyl aromatic compounds and rubbers may be used, and are well known to those skilled in the art. In a polymerizing mixture, some of the vinyl aromatic compound polymerizes to form homopolymer, while the rubber may react with either such homopolymer or with monomer to form grafted copolymer. Impact resistant polymers appear to comprise a mixture of homopolymer and copolymer wherein the copolymer is distributed throughout the mass. Generally, only a small amount of rubber is used, for example, about 10 percent by weight or less, but this is sufficient to impart impact strength to the total polymer mass.